The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An internal mode switch (IMS) is a component of a transmission used to relay the driver's selected range intent to a control system of a vehicle. The conventional IMS assembly, used in vehicles including an automatic transmission, is a mechanical contact configuration. More specifically, the IMS assembly is a sliding contact electrical switch attached to a lower control valve body of the transmission. Conventional switches consist of two major components: a housing, which houses tracks of conductive and non-conductive material that make up stationary contacts, and an insulator assembly, which makes up the moving contacts and is linked to an operator controlled shift lever.
Referring now to FIG. 1, six tracks (A, B, C, Parity, Start, Ground) are shown according to a prior art IMS assembly. The moving contacts pass over tracks that consist of conductive sections (shaded) interrupted by non-conductive sections. For each driving range selected, the moving contacts are in contact with a unique pattern of conductive and non-conductive sections.
When a range is selected, the moving contacts align with conductive and non-conductive sections on the tracks. The IMS assembly independently outputs a signal (usually via wire) for each track to a control system. The signals read by the control system are either a high voltage signal or a low voltage signal. More specifically, the high voltage signal occurs when the moving contact is in contact with a non-conducting material, and the low voltage signal occurs when the moving contact is in contact with a conducting material. The signals produce a unique bit pattern which indicates the selected transmission range.
When using the conventional IMS assembly, fault conditions may not be distinguishable because the signals read by the control system are either a low voltage signal (e.g., 0 volts) or a high voltage signal (e.g., ignition voltage). This may lead to an undesired range indication, which may lead to an undesirable operating condition.
Since the IMS assembly is based on a mechanical configuration, the moving contacts are held against their respective tracks by springs. Due to vehicle motion and/or rough road conditions, the moving contacts may temporarily loose contact with its respective track. This situation is referred to as contact bounce. The control software must account for any contact bounce to ensure a true signal which may result in a time delay when selecting a transmission range. Additionally, mechanical wear and electrical corrosion between the contacts occur. Therefore, each wire outputting a high/low signal includes potential for electrical fault and has material and labor cost associated with it.